The present invention relates to power supplies, and more particularly to redundancy in power supplies.
Redundant AC to DC power supplies are well known in the art. FIG. 1 illustrates a first conventional circuit for providing redundant AC to DC power. The circuit 100 comprises a first AC voltage source 102 coupled to a first power supply 106 in a first power train. The circuit 100 also comprises a second AC voltage source 104 coupled to a second power supply 108 in a second power train. The DC voltages from the first 106 and second 108 power supplies are combined and provided as DC outputs. However, this conventional circuit requires two independent power supplies 106 and 108 connected to two separate AC sources. This adds to the cost of the power system.
FIG. 2 illustrates a second conventional redundant AC power system. The system 200 comprises a first AC voltage source 202 and a second AC voltage source 204. Both sources provide AC voltages to an AC transfer switch 206. The transfer switch 206 supplies either the voltage from the first AC voltage source 202 or the voltage from the second AC voltage source 204 to a power supply 208, which provides DC outputs. However, the transfer switch 206 is very expensive, adding significant cost to the circuit 200.
Accordingly, there exists a need for a low cost redundant AC to DC power supply. This power supply should provide AC power redundancy in a cost effective manner. The present invention addresses such a need.
The power supply in accordance with the present invention provides AC redundancy while also preventing voltages from multiple AC voltage sources from adding at a common node. The adding of voltages is avoided by ensuring that only one AC voltage source at a time is providing the voltage at the output. Even if the other AC voltage sources are connected afterwards, these later AC voltage source are prevented from providing power at the output. In addition, diodes prevent current from back flowing to the AC voltage sources which are not supplying power to the output. Because the power supply in accordance with the present invention neither uses redundant AC to DC power supplies from independent AC voltage sources, nor does it use a costly transfer switch, the power supply in accordance with the present invention is more cost effective than conventional redundant power supplies.